Differential expression of immune checkpoint modulators on in vitro primed CD4+ and CD8+ T cells

Abstract

PD-1, TIM-3, and LAG-3 are molecules shown to have immune modulatory properties, and although initially classified as indicators of T cell hyporesponsiveness, it has become clear that they are also associated with the normal course of T cell activation. Functional studies have focused mainly on CD8+ T cells during chronic inflammation due to interest in co-opting the cellular immune response to eliminate viral or cancerous threats; however, there remains a relative lack of dataregarding the expression of these molecules on CD4+ T cells. Here, we report that expression of the immune checkpoint (IC) molecules PD-1, LAG-3, and TIM-3 are differentially expressed on CD4+ and CD8+ T cells in the allogeneic response resulting from a mixed lymphocyte reaction. In these studies, PD-1 expressionis higher on CD4+ T cells compared to CD8+ T cells. In contrast, TIM-3 is expressed at higher levels on CD8+ T cells compared to CD4+ T cells with an apparent reciprocity in that PD-1+ CD4+ T cellsare frequently TIM-3lo/-, while TIM-3-expressing CD8+ T cells are largely PD-1lo/-. In addition, there is a decrease in the frequency of TIM-3+ CD4+ cells producing IFN-γ and IL-5 compared to TIM-3+ CD8+ cells. Lastly, the memory T cell phenotype within each IC-expressing subset differs between CD4+ and CD8+ T cells. These findings highlight key differences in IC expression patterns between CD4+ and CD8+ T cells and may allow for more effective therapeutic targeting of these molecules in the future.